Melting glaciers contribute to Alaska earthquakes

In 1958, a 7.8 magnitude earthquake triggered a landslide into Lituya Bay in southeastern Alaska, creating a tsunami that was 1,700 feet up a mountainside before running out to sea. The wave was higher than the Empire State Building in New York (1,454 feet – or 443.2 meters – high).

Researchers now believe that the ice area of ​​glaciers lost the platform for the earthquake.

In a recently published research article, scientists from the Geophysical Institute of the University of Alaska Fairbanks found that ice loss near Glacier Bay National Park has affected the time and location of earthquakes with magnitude 5 or more in the area in the last century.

Scientists have known for decades that melting glaciers have caused earthquakes in tectonically stable areas, such as within Canada and Scandinavia. In Alaska, this pattern has become more difficult to detect, as earthquakes are common in the southern part of the state.

Alaska has some of the largest glaciers in the world, potentially thousands of feet thick and covering hundreds of square miles. The pressure of the ice causes the ground beneath to sink, and, when a glacier melts, the ground returns like a sponge.

“There are two parts to the increase,” said Chris Rollins, lead author of the study who conducted the research while at the Geophysical Institute. “This is called the elastic effect, when the earth immediately recovers after a mass of ice is removed. Then the long impact from the mantle flows back above the empty space. ”

Rollins ran models of earth movement and ice loss from 1770, finding a subtle but unique correlation between earthquakes and land reclamation. With the extinction of glaciers, the land of southeastern Alaska increased by about 1.5 inches per year. Suddenly, the greatest pressure occurred from the loss of ice near the very center of the 1958 earthquake that caused the Lituya Bay tsunami.

Although the melting of glaciers is not the direct cause of earthquakes, it does appear to change both the timing and the severity of seismic events.

The distinctive T-shape of Lituya Bay is caused by the Fairweather Fault, crossing the head of the bay from southeast to northwest. As the ground recedes after a glacier recedes, tectonic pressures redistribute, effectively reducing strike cracks, such as the Fairweather, making it easier for both sides to slip past it. each other.

In the case of the 1958 earthquake, the postglacial reaction pushed the crust around the fault in a way that increased pressure near the center as well. Both this and the non-mitigating effect brought the fault closer to failure.

“The movement of blades is the main driver of seismicity, elevation and deformation in the region,” Rollins said. “But postglacial regurgitation adds, like such de-icing on the cake. Cracks in the red zone make it more likely to hit their weight level and slip in an earthquake. ”